Fire and Amphibians in North America

1 Fire and Amphibians in North America David S. Pillioda,* R. Bruce Buryb Erin J. Hydeb Christopher A. Pearlb Paul Stephen Cornc aUSDA Forest Service, Rocky Mountain Research Station Aldo Leopold Wilderness Research Institute PO Box 8089, Missoula, MT 59807 bUSGS Forest and Rangeland Ecosystem Science Center 3200 SW Jefferson Way, Corvallis, OR 97311 cUSGS Northern Rocky Mountain Science Center Aldo Leopold Wilderness Research Institute PO Box 8089, Missoula, MT 59807 *Corresponding Author: David S. Pilliod Aldo Leopold Wilderness Research Institute PO Box 8089, Missoula, MT 59807 Phone: (406) 542-3256; FAX: (406) 542-4196; Email: [email protected] Manuscript accepted to Forest Ecology and Management, to be cited as “in press” Prepublication copy subject to some correction or change. Running Head: Effects of Fire on Amphibians 2 Abstract Information on amphibian responses to fire and fuel reduction practices is critically needed due to potential declines of species and the prevalence of new, more intensive fire management practices in North American forests. The goals of this review are to summarize the known and potential effects of fire and fuels management on amphibians and their aquatic habitats, and to identify information gaps to help direct future scientific research. Amphibians as a group are taxonomically and ecologically diverse; in turn, responses to fire and associated habitat alteration are expected to vary widely among species and among geographic regions. Available data suggest that amphibian responses to fire are spatially and temporally variable and incompletely understood. Much of the limited research has addressed short-term (1-3 yr) effects of prescribed fire on terrestrial life stages of amphibians in the southeastern United States. Information on the long-term negative effects of fire on amphibians and the importance of fire for maintaining amphibian communities is sparse for the high number of taxa in North America. Given the size and severity of recent wildland fires and the national effort to reduce fuels on federal lands, future studies are particularly needed to examine the effects of these landscape disturbances on amphibians. We encourage studies to address population-level responses of amphibians to fire by examining how different life stages are affected by changes in aquatic, riparian, and upland habitats. Research designs need to be rigorous and credible, yet provide information that is relevant for fire managers and those responsible for assessing the potential effects of various fuels reduction alternatives on rare, sensitive, and endangered amphibian species. Keywords: amphibians, aquatic ecosystems, fuel reduction, prescribed fire, wildland fire 3 Introduction The extensive and damaging fires of 2000 and 2002 that burned across large portions of western and southeastern North America have increased public awareness of the consequences of large fires. This national attention has resulted in fire and forest management policy changes on private, state, and federal lands. In 2001, a National Fire Plan (NFP) was approved by Congress to reduce fire risk and to restore healthy fire-adapted ecosystems on federal lands through proactive fuel reduction (USDA and USDI, 2001). One problem with implementing NFP objectives is that large information gaps exist regarding effects of proposed fuel-reduction practices (e.g., prescription burning and mechanical fuel reduction) on native flora and fauna. Most fuel reducing activities on federal lands require ecological assessments, as mandated by the National Environmental Protection Act (NEPA), that require information on potential responses of species to proposed management practices. Until recently, such information has been poorly represented in peer-reviewed literature and has not been summarized. Amphibians are of particular conservation concern because many species have restricted geographical ranges, occur only in localized microhabitats that may be vulnerable to management activities, or are listed under the Endangered Species Act (Semlitsch, 2000). Many amphibian species have declined across large portions of their range throughout the United States (Corn, 2000). Information on amphibian responses to fire and fuel reduction practices is needed to assist managers in determining whether an event or action is beneficial or harmful. However, most studies of the effects of fire on amphibians have recorded responses of terrestrial species or terrestrial life stages of aquatically breeding species to prescription burning in the southeastern United States or Australia (Table 1; see reviews by deMaynadier and Hunter, 1995; Russell et al., 1999). Bury et al. (2002) summarized potential responses of amphibian 4 distribution and abundance to fire in the Pacific Northwest and compared patterns using a chronosequence of forest stands. Few studies offered insight into the effects of fire on aquatic habitats of amphibians. The primary goal of this paper is to extend prior reviews by providing a more detailed summary of observed and potential effects of wildland fires, fuel reduction practices, and associated management activities on aquatic habitats of amphibians and species that breed in aquatic habitats throughout North America. Hence, this review focuses on those species that require water in one or more life stage (which essentially means all species except plethodontid salamanders). Further, we provide new information from recent literature and ongoing studies, and offer a framework for identifying information gaps and directing future scientific research to examine amphibian responses to fire and fire-related habitat changes. Characteristics of Amphibians and Their Habitats that Influence Responses to Fire Amphibians are a diverse group of animals with complex life cycles and many have evolved and persisted in fire prone regions, possibly due to adaptations to fire disturbances. Some pond-breeding species in forests with high frequency fire regimes (e.g., southeastern Coastal Plain) rely on the heterogeneous landscapes and open conditions created and maintained by fire for long-term population stability (Dodd, 1997; Brennan et al., 1998; Greenberg, 2002). Conversely, species that have narrow geographic distributions, are closely tied to specific microhabitat conditions (e.g., soil or water temperatures, or cover types), or occur in areas with very long fire-return intervals may be adversely affected by fire. Factors such as timing of reproduction, duration of larval period, vagility, and resistance to desiccation are characteristics that may determine a species’ response to fire. A few species of amphibians remain in water 5 during all life stages (Dodd, 1997). Most species breed in aquatic environments but juveniles and adults spend some time on land where they may be particularly vulnerable to fire-related mortality and habitat disturbances. Ecological sensitivity analyses have indicated that mortality of juveniles and adults would likely have the strongest influence on population dynamics of some species of frogs and toads (Biek et al., 2002). Thus, the sensitivity of amphibians to fire disturbances will likely vary among life stages, among populations in different geographic regions, and certainly among species that have evolved under different environmental conditions and fire regimes. Fire-related disturbances operate across multiple habitats and spatial scales. Individual animals or small populations may respond to disturbances at the microhabitat level, where fires eliminate or alter important amphibian cover through combustion of understory vegetation and surface materials, or filling of interstitial spaces in aquatic substrates with ash and sediment. At the macrohabitat level (e.g., lake, pond, stream), fires may increase solar radiation and water temperatures, alter hydroperiods and nutrient cycling, and enhance productivity. Landscape attributes such as the spatial distribution of amphibian habitat in a watershed may influence the resistance and resilience of a population to disturbance. For example, many amphibians that breed in isolated water bodies will travel hundreds to thousands of meters away from water seasonally (Dodd, 1996; Hayes et al., 2001; Pilliod et al., In Press). Moreover, amphibian populations may function as metapopulations, and local fluctuations, extirpations, and dispersal patterns can be linked across a landscape (Marsh and Trenham, 2001). 6 Effects of Fire on Amphibians Available data suggest that amphibian responses to fire and associated habitat alteration are species-specific, incompletely understood, and variable among habitats and regions (Appendix 1). Wildland and prescribed fires may affect amphibian populations either directly (e.g., killing individuals) or indirectly (e.g., habitat alteration), and effects likely vary relative to time since burning (Gresswell, 1999). Biotic responses to fire can be partitioned into immediate (during and days after a fire), short-term (<1 yr), mid-term (1-10 yrs), and long-term (>10 yrs) effects (Minshall et al., 1997). Public impressions of fire are often based upon immediate and short-term visible effects associated with news media-covered conflagrations. These effects are usually short in duration, whereas other less dramatic indirect effects can alter ecosystems for years and even decades. Indirect effects of fires on amphibians result from changes in habitat structure and ecosystem function. Most investigations into the effects of fire on amphibians have been of short-

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